This application is a request for 5 years funding to continue studies on the molecular biology, biochemistry, and cell biology of the newly described cell adhesion molecule, PECAM-1 (formerly known as GP130).The first aim is to examine the biochemical events that control expression and activation of PECAM-1. Changes in expression of PECAM-1 protein and its mRNA transcript in response to cytokine stimulation will be quantitated and correlated with morphological changes and adhesive properties of human endothelial cells, leukocytes, and certain transformed cell lines. Post-translational events, including phosphorylation and lipid modification will also be examined to determine whether these might modulate the adhesive properties or subcellular distribution of PECAM-1. The second aim is to examine the function of PECAM-1. Solid-phase microtiter cell adhesion assays will be used to examine in detail the interactions of platelets, monocytes, neutrophils, and certain tumor cell lines with endothelial cell monolayers and with stable transfected cell lines expressing PECAM-1. Anti-PECAM-1 antibodies, short synthetic peptides, and recombinant soluble PECAM-1 will be examined for their ability to interfere with these cellular interactions. In addition to these studies, we will seek to identify the cellular receptor(s) for PECAM-1. The third aim is to characterize the size, chromosomal organization, chromosomal location, and number of genes that encode PECAM-1. Chromosomal localization will be determined by PcR amplification of human chromosome-specific libraries and/or by screening a panel of human/hamster somatic cell hybrids that contain known subsets of human chromosomes. Gene fine structure, including a restriction map, intron/exon boundaries, and the potentially important 5' regulatory region, will be deduced by analysis of genomic clones obtained by screening human genomic DNA libraries with radiolabeled PECAM-1 cDNA probes.